Crystal structures and magnetic interactions in nickel(II) dibridged complexes formed by both phenolate oxygen-azide, or methanlate groups

Article abstract of DOI:10.1007/s11243-010-9403-9

Tridentate Schiff base ligands L¹ and L², derived from the condensation of 2-hydroxy-3-methox-ybenzaldehyde (L) with 2-aminoethanol or 2-aminobutan-1-ol, react with nickel chloride, azide, or thiocyanate to give rise to two dinuclear

Full text of DOI:10.1007/s11243-010-9403-9

Transition Met Chem (2010) 35:851–858
DOI 10.1007/s11243-010-9403-9
Crystal structures and magnetic interactions in nickel(II)
dibridged complexes formed by both phenolate oxygen-azide,
or methanlate groups
Yan Zhang
Wen-Guo Xu
•
Xiao-Man Zhang
•
Tian-Fu Liu
•
Received: 1 June 2010 / Accepted: 16 July 2010 / Published online: 3 August 2010
Ó Springer Science+Business Media B.V. 2010
1
2
Abstract Tridentate Schiff base ligands L and L ,
derived from the condensation of 2-hydroxy-3-methox-
ybenzaldehyde (L) with 2-aminoethanol or 2-aminobutan-
N-alkyl- and N-aryl-salicylideneimines. When Ni(II) atoms
coordinate to these ligands in 1:1 mode, the coordination
sphere of Ni(II) remains unsaturated, and the resulting
mononuclear coordination moieties can further oligomerize
with the aid of bridging groups affording binuclear or
polynuclear complexes. Because of the rich coordination
modes and an efficient pathway of magnetic exchange, the
azido bridge has aroused considerable interest in the past
decade. Complexes with novel magnetic properties have
been prepared by using this anion, and their magneto-
structural correlations have been extensively studied. To
date, the azido ligand has been found to bridge metal ions
in the modes of l1,1-(end-on, EO)[18–22], l1,3-(end-
to-end, EE) [23, 24], l1,1,3 [25–27], l1,1,1 [28], l1,1,1,1
[29, 30], l1,1,3,3 [31, 32] or unusual l1,1,1,3,3,3 fashions [33]
1
-ol, react with nickel chloride, azide, or thiocyanate to
give rise to two dinuclear complexes of formulas [Ni (L)-
2
1
2
(
L ) N ]ꢀH O (1), [Ni (L ) (l -N )]ꢀ2H O (2), and one
2
3
2
2
3
1,1
3
2
2
tretranuclear complex [Ni (L ) (NCS)] (C H OH) (3),
2
2
2
2
5
2
1
-
where L = HOCH CH(C H )NCHC H (O )(OCH ) and
2
2
5
6
3
3
2
L = HO(CH ) NCHC H (O )(OCH ). We have charac-
-
2
2
6
3
3
terized these complexes by analytical, crystal structures,
and variable temperature magnetic susceptibility mea-
surements. The magnetic properties of the complexes are
studied by magnetic susceptibility (v ) vs. temperature
measurements. The v T vs. T plots reveal that compounds
M
M
1
, 2 and 3 are ferromagnetically coupled.
(Scheme 1). Ferromagnetic interactions are usually trans-
mitted by the EO bridging mode of the azido ligand as are
antiferromagnetic interactions by the EE bridging mode
Introduction
[
34].
Herein, we report the syntheses, crystal structures and
Hetero- and homo-binuclear complexes of Ni(II) have
attracted much attention over recent years due to their
relevance to the active sites of metalloenzymes [1–4], and
potential applications as optical [5, 6], electronic, and
molecule-based magnetic materials [7–13]. The structures
of the products are dependent on many factors, such as the
structure of chelating ligands [14–16], metal centers,
anions, and solvents [17]. Numerous papers have so far
been published concerning nickel(II) complexes of
magnetic properties of three nickel complexes: two dinu-
clear Ni(II) complexes with Phenolate Oxygen-Azide
1
2
bridge [Ni (L)(L ) N ]ꢀH O (1) and [Ni (L ) (l -N )]ꢀ
2
2
3
2
2
3
1,1
3
2
2H O (2), and one tretranuclear complex [Ni (L ) (NCS)] -
2
2
2
2
(C H OH) (3). Their magnetic properties have been studied
2
2
5
and correlated with molecular structures.
Experimental section
Materials and instrumentation
Y. Zhang ꢀ X.-M. Zhang ꢀ T.-F. Liu (&) ꢀ W.-G. Xu
Department of Chemistry & Key Laboratory of Cluster Science
of Ministry of Education, Beijing Institute of Technology,
100081 Beijing, People’s Republic of China
e-mail: liutf@bit.edu.cn
All chemicals and solvents were of analytical grade and
used as received without further purification. The Schiff
1
base (Scheme 2) H2L was obtained by refluxing an
123

8
52
Transition Met Chem (2010) 35:851–858
Scheme 1 Azide bridging
modes
∗
N
N
OH
OH
OH
OH
OMe
OMe
1
2
H L =(E)-2-((1-hydroxybutan-2-ylimino)methyl)-6-methoxyphenol H L =(E)-2-((2-hydroxyethylimino)methyl)-6-methoxyphenol
2
2
1
2
2 2
Scheme 2 The structures of H L and H L ligands
2
(L )
2
ethanolic solution of o-vanillin and racemic 2-aminobutanol
for 2 h. The resulting orange–yellow solution containing
Preparation of [Ni
2
2
(HL )(l1,1-N
3
)]ꢀ2H
O (2)
2
the Schiff base was used without further purification. The
2
ligand H L was prepared by a method similar to that of
The procedure was the same as that for the dimer described
above, except for the ligand, for which 6 mL of an etha-
2
L (0.3 mmol) was used. Green block
2
1
H L by using o-vanillin and racemic 2-ethanolamine. All
nolic solution of H
2
2
preparations and manipulations were performed under
aerobic conditions. Infrared spectra were recorded as KBr
pellets with a Perkin–Elmer Spectrum One FT-IR spectro-
crystals were obtained after 10 days. Crystals were filtered
out and air-dried. Anal. Calc for C30 Ni 12: C, 45.2;
H
42
N
O
2
6
H, 5.7; N, 10.6%. Found: C, 45.0; H, 5.6; N, 10.7%. IR
-1
(KBr pellet,cm ): 3,429 br, 2,929 br, 2,833 w, 2,364 br,
-
1
photometer in the range 4,000–400 cm
.
Caution! Azide compounds are potentially explosive!
Only a small amount of material should be prepared and
handled with care.
2,065 vs, 1,637 vs, 1,601 m, 1,543 br, 1,468 s, 1,445 s,
1,406 m, 1,320 m, 1,302 m, 1,240 s, 1,213 vs, 1,167 w,
1,084 m, 1,054 m, 971 m, 741 s.
1
2
(L )
2
(HL )
Preparation of [Ni (L ) (l -N )(o-vanillin)]ꢀH O (1)
Preparation of [Ni
2
2
2
(NCS)
2
(EtOH)
2
]
2
ꢀEtOH (3)
2
2
1,1
3
2
1
To a solution of H L (0.3 mmol) in 6 mL ethanol was
The procedure was the same as that for the dimer described
2
added dropwise a solution of NiCl ꢀ6H O (74.3 mg,
above, except for the ligand, for which 6 mL of an ethanol
2
L (0.3 mmol) was used. The green reaction
2
2
0
.3 mmol), and the mixture was stirred for about 1 h at
solution of H
2
room temperature. Then, an aqueous solution (5 mL) of
mixture was stirred for a few minutes after which a solution
of NH SCN (34.3 mg, 0.45 mmol) in MeOH (5 mL) was
NaN (0.3 mmol) was added dropwise. After 30 min of
3
4
stirring, the resulting solution was obtained. The mixture
was allowed to stand at room temperature without any
further disturbance for several days to give green block
crystals. Anal. Calc for C H N Ni O : C, 49.7; H, 5.3;
added, and the mixture was stirred for an additional 15 min
and filtrated. The resulting filtered was allowed to stand for
a few days during which green single crystals were
obtained. Anal. Calc for C48.4H N Ni O S : C, 45.1;
66.78 6 4 16 2
3
2
41
5
2 10
N, 9.1%. Found: C, 51.1; H, 5.1; N, 8.8%. IR (KBr pel-
H, 5.2; N, 6.5%. Found: C, 45.3; H, 5.2; N, 6.7%. IR
-1
(KBr pellet,cm ): 3,406 br, 2,930 br, 2,864 br, 2,104 vs,
-
1
let,cm ): 3,501 br, 2,967 br, 2,932 br, 2,684 w, 2,069 vs,
,637 vs, 1,601 s, 1,545 m, 1,469 s, 1,442 s, 1,408 m, 1,322
m, 1,240 s, 1,211 vs, 1,167 w, 1,131 br, 1,106 w, 1,077 m,
,039 w, 975 w, 963 w, 738 s, 604 br.
1
1,631 vs, 1,600.85 m, 1,547 w, 1,469 s, 1,443 s, 1,401 m,
1,353 w, 1,319 m, 1,244 s, 1,213 vs, 1,168 w, 1,080 m,
1,056 m, 971 m, 902 br, 856 m, 784 w, 747 s, 637 br.
1
1
23

Transition Met Chem (2010) 35:851–858
X-ray crystallography
853
structure is presented in Table 1. The structure of the
molecular unit is shown in Fig. 1a. Selected bond lengths
and angles of complex 1 are collated in Table 2. The unit
includes one independent dimeric complex molecule and
one crystal water. The complex has a dinickel(II) structure
A single crystal was used for X-ray diffraction analysis.
Determination of the unit cell and data collection was
performed on a Bruker SMART 1,0009 diffractometer
using graphite monochromated Mo-K radiation at 293(2)
a
with one azide group in end-on fashion through N and one
3
K. The structure was solved by direct methods in SHEL-
XS-97 [35] and refined using a full-matrix least squares
deprotonated l -phenolate oxygen atom O of o-vanillin
2
5
bridges. Each nickel(II) atom is coordinated to one ligand
1
H L (Scheme 1a), which acts in a tridentate mode, with
2
procedure on F in SHELXS-97 [36]. The disordered C ,
1
7
2
C18, C , N and O6 sites were refined with an equal
19
one amino N, one deprotonated phenoxo O atom and one
2
occupation factor of 0.5; and C22 was refined with three
positions with occupation factor of 0.419, 0.384 and 0.197;
and C , C and O were refined with the occupation
ethanol O atom coordinated. The remaining alkoxyl O
1
atom of H L is left noncoordinated in a neutral form. One
2
2
3
24
8
o-vanillin molecule is contained, with aldehyde oxygen
atom O coordinated to Ni and alkoxyl O atom coordi-
factor of 0.556 and 0.444 for compound 3. All H atoms
could be located in the difference Fourier map and refined
without constraints.
4
1
6
nated to Ni . The basal bond distances around the Ni atom
2
1
˚
are in the 2.111(9)–1.997(5) A range, and the apical bond
˚
distances are 2.084(5) and 2.146(3) A, respectively. The
Magnetic measurements
bond distances around the Ni atoms are in the 2.124(1)–
2
˚
1.992(1) A range, and the apical bond distances are
˚
2.099(9) and 2.219(2) A. The axial bond angle O -Ni -N
4 1 3
Magnetic data were recorded using a Quantum Design
SQUID magnetometer. To avoid orientation in the mag-
netic field, the samples were pressed in a home-made
Teflon sample holder equipped with a piston. The data
were corrected for diamagnetism of the constituent atoms
using Pascal’s constants.
has a small value of 163.32(9)°, and the other axial bond
angle O -Ni -N has a smaller value of 152.41(7)°, indi-
6
2
3
cating severe distortions of the octahedral configurations.
The major distortion from a ‘‘regular’’ octahedron for two
nickel centers could be the result of the bridging azide and
phenolate group. The largest bond between Ni and O is
2
6
most probably due to the bonding of the phenolate oxygen
atom of the same ring and to the coordination of hydroxyl
Results and discussion
group. The bridging O atom has almost equivalent bond
5
˚
lengths of 2.022(9) and 2.016(2) A with Ni and Ni2,
Description of the crystal structures
1
respectively. The bridging N atom has slightly longer
3
1
˚
bond lengths of 2.146(3) and 2.099(9) A with Ni and Ni .
[
Ni (L ) (l -N )(o-vanillin)]ꢀH O
2
2
1,1
3
2
1
2
Ni -O -Ni bridging angle is 104.63(7)°, and Ni -N -Ni
1
5
2
1
3
2
Single-crystal X-ray diffraction of 1 (Fig. 1) reveals that it
ꢀ
crystallizes in the triclinic space group P 1, and the
bridging angle is 97.66(5)°. The nickel(II) centers are
˚
separated by 3.196(7) A.
2
2
[
Ni (L ) (HL )(l -N )]ꢀ2H O
2
2
1,1
3
2
The crystal structure of complex 2 includes one indepen-
dent dimeric complex molecule and two H O molecules
2
(
Fig. 2). Selected bond lengths and angles of complex 2 are
collated in Table 3. The dinuclear unit is formed by two
Ni(II) atoms labeled Ni and Ni , bridged by one azide
1
2
group in end-on fashion through N and one l -phenolate
6
2
oxygen atom O of the Schiff base. The coordination sites
1
of the octahedral Ni atom are completed by one nitrogen
1
atom N and two oxygen atoms O and O of the same
2
4
9
Schiff base ligand and by a nitrogen atom N3 of the
bridging moiety. Similarly, the remaining sites of distorted
octahedral geometry of Ni2 atom are occupied by one
nitrogen atom N and two oxygen atoms O and O of the
1
5
7
Fig. 1 The molecular structure (30% thermal probability ellipsoids)
of complex 1 showing the atom numbering (hydrogen atoms and
waters are omitted for clarity)
same Schiff base ligand and a methoxy oxygen atom O of
2
the bridging Schiff base. Deviation of the Ni and Ni
1
2
123

8
54
Transition Met Chem (2010) 35:851–858
Table 1 Crystal data and
details of the structure
determination
Compound
Formula
1
C
2
C
3
32
H
41 5
N Ni
O
2 10
30 42 6
H N Ni
O
2 12
48.4 66.78 6 4 16 2
C H N Ni O S
-1
]
Mr[g mol
773.08
293(2)
796.12
293(2)
1287.56
77(2)
T[K]
˚
k[A]
0.71073
Triclinic
0.71073
Triclinic
0.71073
Crystal system
Space group
Monoclinic
/c
ꢀ
P1
ꢀ
P1
C
2
˚
a[A]
10.315(2)
12.766(2)
13.781(2)
71.999(5)
76.521(5)
85.040(5)
1678.2(5)
2
10.140(2)
11.456(2)
15.398(3)
91.47(3)
96.10(3)
96.05(3)
1767.4(6)
2
24.660(5)
19.636(4)
11.314(2)
90
˚
b[A]
˚
c[A]
a[°]
b[°]
c[°]
90.957(3)
90
3
˚
V[A ]
5477.6(2)
8
Z
-
3
]
q
calcd [g cm
1.530
1.458
1.561
-
1
]
l [mm
F(000)
1.187
1.130
1.503
808
832
2,685
Crystal size [mm]
0.33 9 0.30 9 0.23 0.12 9 0.10 9 0.08 0.33 9 0.23 9 0.20
h[°]
3.07–27.48
13,646
1.79–25.30
10,155
3.19–27.47
22,173
Measured reflections
Unique reflection
R(int.)
7,384
6,879
6,181
0.0251
0.0174
0.0315
Completeness [%]
Data/restaints/parameters
GOF on F2
95.7 (h = 27.48)
7,384/1/463
0.998
97.9 (h = 25.30)
6,879/6/479
1.008
98.4(h = 27.47)
6,181/33/433
0.997
R
1
[I [ 2r(I)]
wR [I [ 2r(I)]
(all data)
wR (all data)
Largest diff. peak and hole [eA
0.0477
0.0554
0.0489
2
0.1191
0.1534
0.1207
R
1
0.0569
0.0867
0.0558
2
0.1126
0.1671
0.1269
-3
]
˚
0.81, -0.69
0.87, -0.52
0.96, -0.93
atoms from the mean plane formed by the three oxygens
Selected bond lengths and angles of complex 3 are collated
in Table 4. The centrally symmetric unit includes one
independent tetranuclear complex molecule and one etha-
nol molecule as crystallization solvent. The complex
molecule consists of an arrangement of four nickel atoms,
four deprotonated accessory ligands and four terminal
and one nitrogen atom of Ni and by one nitrogen and three
1
˚
oxygen atoms of Ni are 0.0768 and 0.0377 A, respec-
2
tively. The basal bond distances around the Ni atom are
1
˚
in the 2.116(3)–1.980(5) A range, and the apical bond
˚
distances are 2.091(9) and 2.190(4) A, respectively con-
-
sidering the bond angle N -Ni -N = 166.09(1)°. The bond
monodentate ligands (two NCS and two methanol mole-
3
1
6
˚
distances around the Ni atom are in the 2.154–1.979 A
cules). Four Ni and four O atoms including two phenolate
O atoms (O and O A) and two alkoxide O atoms (O and
2
range. The apical bond distances are 2.088(0) and
˚
3
3
4
2
.240(0) A considering the bond angle O -Ni -N =
2
O A) occupy the vertices of a distorted {Ni (l -O) }
2
6
4
4
3
4
1
52.47(0)°. The major distortion could arise from the same
cubane core. Ni1 and Ni A are arranged in the same
1
reason as complex 1. Ni -O -Ni bridging angle is
1
˚
distance between Nickel(II) centers is 3.184(9) A.
manner, the coordination sphere of each completed by
three bridging O atoms, one phenolate O atoms, one alk-
1
1
2
06.36(1)° and Ni -N -Ni bridging angle is 96.21(2)°.The
1
6
2
2
oxyl O atom and one amino N atom from (L2) and with
-
˚
the Ni-O bond length in the range of 1.980(2)–2.292(2) A
2
2
˚
and Ni-N bond length of 1.977(2)A. Ni and Ni A are in
[
Ni (L ) (HL ) (NCS) (EtOH) ] ꢀEtOH
2
2
2
2
2 2
2
2
the same coordination sphere, including three bridging O
atoms, one O atom from the methanol ligand, one amino
Compound 3 crystallizes in the monoclinic space group
C /c, and the molecular structure is shown in Fig. 3.
2
N atom from (HL ) and one N atom from NCS with the
-
-
2
1
23

Transition Met Chem (2010) 35:851–858
855
˚
Table 2 Selected bond lengths (A) and angles (deg) for compound 1
˚
Table 3 Selected bond lengths (A) and angles (deg) for compound 2
Ni(1)-O(1)
1.998(2)
2.001(3)
2.022(2)
2.085(2)
2.112(2)
2.146(2)
97.66(10)
91.30(9)
95.81(8)
170.24(9)
91.24(8)
99.58(10)
86.97(9)
171.28(8)
80.48(9)
92.70(8)
87.30(8)
91.11(9)
96.84(10)
76.39(9)
163.35(9)
92.74(9)
Ni(2)-O(7)
1.993(2)
1.993(3)
2.017(2)
2.100(2)
2.124(2)
2.219(2)
104.61(9)
91.51(9)
102.02(8)
165.34(9)
95.51(9)
107.02(10)
77.56(9)
171.15(8)
80.56(9)
85.53(8)
90.60(9)
87.59(8)
100.28(10)
74.98(8)
152.41(9)
89.95(8)
Ni(2)-N(1)
1.979(5)
1.989(3)
Ni(1)-O(1)
1.987(3)
1.981(4)
Ni(1)-N(1)
Ni(2)-N(2)
Ni(2)-O(5)
Ni(1)-N(2)
Ni(1)-O(5)
Ni(2)-O(5)
Ni(2)-O(1)
1.992(4)
Ni(1)-O(4)
2.017(4)
Ni(1)-O(4)
Ni(2)-N(3)
Ni(2)-N(6)
2.088(4)
Ni(1)-N(3)
2.092(5)
Ni(1)-O(3)
Ni(2)-O(9)
Ni(2)-O(7)
2.154(3)
Ni(1)-O(9)
2.117(4)
Ni(1)-N(3)
Ni(2)-O(6)
Ni(2)-O(2)
2.240(4)
Ni(1)-N(6)
2.190(4)
Ni(2)-N(3)-Ni(1)
O(1)-Ni(1)-N(1)
O(1)-Ni(1)-O(5)
N(1)-Ni(1)-O(5)
O(1)-Ni(1)-O(4)
N(1)-Ni(1)-O(4)
O(5)-Ni(1)-O(4)
O(1)-Ni(1)-O(3)
N(1)-Ni(1)-O(3)
O(5)-Ni(1)-O(3)
O(4)-Ni(1)-O(3)
O(1)-Ni(1)-N(3)
N(1)-Ni(1)-N(3)
O(5)-Ni(1)-N(3)
O(4)-Ni(1)-N(3)
O(3)-Ni(1)-N(3)
Ni(2)-O(5)-Ni(1)
O(7)-Ni(2)-N(2)
O(7)-Ni(2)-O(5)
N(2)-Ni(2)-O(5)
O(7)-Ni(2)-N(3)
N(2)-Ni(2)-N(3)
O(5)-Ni(2)-N(3)
O(7)-Ni(2)-O(9)
N(2)-Ni(2)-O(9)
O(5)-Ni(2)-O(9)
N(3)-Ni(2)-O(9)
O(7)-Ni(2)-O(6)
N(2)-Ni(2)-O(6)
O(5)-Ni(2)-O(6)
N(3)-Ni(2)-O(6)
O(9)-Ni(2)-O(6)
Ni(2)-N(6)-Ni(1)
N(1)-Ni(2)-O(5)
N(1)-Ni(2)-O(1)
O(5)-Ni(2)-O(1)
N(1)-Ni(2)-N(6)
O(5)-Ni(2)-N(6)
O(1)-Ni(2)-N(6)
N(1)-Ni(2)-O(7)
O(5)-Ni(2)-O(7)
O(1)-Ni(2)-O(7)
N(6)-Ni(2)-O(7)
N(1)-Ni(2)-O(2)
O(5)-Ni(2)-O(2)
O(1)-Ni(2)-O(2)
N(6)-Ni(2)-O(2)
O(7)-Ni(2)-O(2)
96.21(16)
90.99(17)
165.65(17)
103.33(15)
101.47(17)
94.49(16)
78.73(14)
79.83(17)
170.33(14)
85.83(15)
90.32(15)
105.66(17)
89.68(14)
73.83(14)
152.46(16)
89.92(14)
Ni(1)-O(1)-Ni(2)
O(1)-Ni(1)-N(2)
O(1)-Ni(1)-O(4)
N(2)-Ni(1)-O(4)
O(1)-Ni(1)-N(3)
N(2)-Ni(1)-N(3)
O(4)-Ni(1)-N(3)
O(1)-Ni(1)-O(9)
N(2)-Ni(1)-O(9)
O(4)-Ni(1)-O(9)
N(3)-Ni(1)-O(9)
O(1)-Ni(1)-N(6)
N(2)-Ni(1)-N(6)
O(4)-Ni(1)-N(6)
N(3)-Ni(1)-N(6)
O(9)-Ni(1)-N(6)
106.36(14)
168.03(17)
95.64(14)
91.62(17)
89.76(17)
99.30(18)
93.57(18)
92.14(15)
80.51(17)
172.13(14)
87.67(18)
76.42(14)
94.18(16)
89.48(16)
166.08(18)
91.16(15)
Fig. 3 The molecular structure (30% thermal probability ellipsoids)
of complex 3 showing the atom numbering (only one position of
disorder atoms C17, C18, C19, N and O are shown, hydrogen atoms
2 6
and ethanol molecule are omitted for clarity). Symmetry transforma-
tions used to generate equivalent atoms: #A - x ? 1, y, -z ? 3/2
Fig. 2 The molecular structure (30% thermal probability ellipsoids)
of complex 2 showing the atom numbering (hydrogen atoms and
waters are omitted for clarity)
Ni-O and Ni-N bond lengths in the range of 2.014(2)–
˚
˚
the distance of 3.0574(6) A between Ni1 and Ni equal to
2
.101(3) and 1.992(3)–2.053(3) A. Among the Ni-O dis-
2
tances corresponding to the oxygen atoms that belong to
˚
the cubane core, Ni -O A (2.275(3)A) and Ni A-O
the distance between Ni A and Ni A is the shortest, and the
1
˚
distance of 3.3890(9) A between Ni and Ni A is the lon-
2 2
2
2
4
2
4
˚
2.275(3)A) are slightly longer than other two Ni-O bonds
(
gest. The main distortion of the cubane core is also due to
˚
ranging from 2.014(2) to 2.074(2)A. In this elongated cube,
the differences in Ni-O-Ni angles which average 103.93° in
123

8
56
Transition Met Chem (2010) 35:851–858
˚
Table 4 Selected bond lengths (A) and angles (deg) for compound 3
(a)
Ni(1)-N(1)
1.977(2) Ni(2)-N(3)
1.980(2) Ni(2)-O(4)
1.992(3)
2.014(2)
2.0520(19)
2.053(3)
2.101(3)
2.275(3)
83.56(9)
160.28(11)
82.42(9)
3
3
2
2
.25
.00
.75
.50
Ni(1)-O(1)
Ni(1)-O(3)
2.040(2) Ni(2)-O(3)#1
2.042(2) Ni(2)-N(2)
Ni(1)-O(4)
Ni(1)-O(3)#1
2.074(2) Ni(2)-O(7)
Ni(1)-O(5)
2.292(2) Ni(2)-O(4)#1
92.27(9) N(1)-Ni(1)-O(3)
172.54(8) N(1)-Ni(1)-O(4)
103.06(9) O(3)-Ni(1)-O(4)
T
N(1)-Ni(1)-O(1)
O(1)-Ni(1)-O(3)
O(1)-Ni(1)-O(4)
N(1)-Ni(1)-O(3)#1
O(3)-Ni(1)-O(3)#1
N(1)-Ni(1)-O(5)
O(3)-Ni(1)-O(5)
O(3)#1-Ni(1)-O(5)
N(3)-Ni(2)-O(3)#1
N(3)-Ni(2)-N(2)
O(3)#1-Ni(2)-N(2)
O(4)-Ni(2)-N(2’)
χ
110.78(9) O(1)-Ni(1)-O(3)#1 93.66(9)
82.11(9) O(4)-Ni(1)-O(3)#1 80.91(8)
0
50
100
150
200
250
300
96.19(8) O(1)-Ni(1)-O(5)
100.32(8) O(4)-Ni(1)-O(5)
153.01(7) N(3)-Ni(2)-O(4)
86.24(9)
72.87(7)
T
/ K
173.00(11)
(
b) 3.4
3.2
94.78(9) O(4)-Ni(2)-O(3)#1 82.12(8)
96.2(3)
165.8(4)
89.7(3)
O(4)-Ni(2)-N(2)
N(3)-Ni(2)-N(2’)
85.9(3)
93.6(3)
O(3)#1-Ni(2)-
N(2’)
171.6(3)
N(2)-Ni(2)-N(2’)
O(4)-Ni(2)-O(7)
N(2)-Ni(2)-O(7)
N(3)-Ni(2)-O(4)#1
10.2(8)
N(3)-Ni(2)-O(7)
97.21(11)
3.0
88.94(10) O(3)#1-Ni(2)-O(7) 87.25(9)
100.1(5) N(2’)-Ni(2)-O(7) 90.7(5)
T
χ
2.8
97.76(10) O(4)-Ni(2)-O(4)#1 75.45(9)
76.65(8) N(2)-Ni(2)-O(4)#1 93.0(5)
O(3)#1-Ni(2)-
O(4)#1
N(2’)-Ni(2)-O(4)#1 103.2(5)
O(7)-Ni(2)-O(4)#1 158.83(8)
2.6
0
50
100
150
200
250
300
Ni(1)-O(3)-Ni(2)#1 103.61(9) Ni(1)-O(3)-
Ni(1)#1
97.46(9)
97.83(9)
96.16(9)
T
/ K
Ni(2)#1-O(3)-
Ni(1)#1
95.62(8) Ni(2)-O(4)-Ni(1)
Fig. 4 a Plot of v
line represents the best fit of the experimental data
M
T vs. T for 1. b Plot of v T vs. T for 2. The solid
M
Ni(2)-O(4)-Ni(2)#1 104.23(9) Ni(1)-O(4)-
Ni(2)#1
temperature. This behavior with the decrease in v T at low
M
temperatures is attributed to either interdinuclear antifer-
romagnetic interactions and/or the effect of the zero-field
splitting (ZFS) of the S = 1 ground state. The cryomag-
netic behavior of 1 and 2 obeys the Curie–Weiss law in the
Symmetry transformations used to generate equivalent atoms:
1 - x ? 1, y, -z ? 3/2
#
the case of Ni -O -Ni A and Ni -O -Ni A while the other
2
1
3
2
2
4
3
Ni-O-Ni angles are around 95.63–97.84°.
temperature region 50–300 K, yielding C = 2.72 cm
3
-
1
-1
K mol , h = 8.02 K for 1 and C = 2.76 cm K mol
h = 8.11 K for 2.
The experimental data were fitted with the following
,
Magnetic measurements
The magnetic susceptibilities of complexes 1 and 2 shown
in Fig. 4 were measured at 0.1 T in the temperature range
expression, derived from the Van Vleck formula (H =
-
JS S ) for two S = 1 ions and modified for inclusion of
1 2
2
.0–300 K for 1 and 5.0–300 K for 2. 1 and 2 exhibit the
similar magnetic properties. Plots of v T vs. T for 1 and 2
the zero-field splitting parameter (D) in the ground state.
M
2
2
Ng b
(
Fig. 4) show typical ferromagnetic behaviors: an increase
vMT ¼
fðxÞ þ TIPT:
k
ð1Þ
3
in the effective magnetic moment with decreasing tem-
3
M
-1
perature. The v T product at 300 K (2.77 cm mol K for
with
3
-1
1
and 2.92 cm mol K for 2) is on the order of the
expected one for two uncoupled Ni(II) ions, with g about
.2, and this value increases upon cooling to reach a
ꢁ
2J=kT
D=kT
ꢁ2D=kT
2
e
þ 6e
þ 24e
fðxÞ ¼ 3 ꢁ
2J=kT
þ eꢁ3J=kT þ e
2D=kT D=kT
þ 2eꢁ2D=kT
where the symbols have their usual meaning, and the last
e
þ 2e
2
3
-1
maximum at 30 K (3.32 cm mol
K) for 1 (31 K
3 -1
3.35 cm mol K) for 2) then diminishes with decreasing
(
term (TIP) is the temperature-independent paramagnetism.
1
23

Transition Met Chem (2010) 35:851–858
857
-
1
6
4
3
1
0
0
5
0
5
to the data leads to g = 2.27, J = -1.26 cm , J =
A B
-1
-5
3
-1
1.92 cm , TIP = 1 9 10 cm mol , R = 1.21 9 10
-6
6
5
P ꢀ
ꢁ
P
2
2
(R ¼
ðv Þ ꢁ ðv Þ
=
½ðv Þ ꢂ ). The negative
M obs
M calc
M obs
χ
J and positive J are in good agreement with the
structural feature described above.
A
B
Tetranuclear Ni O cubane complexes have proven to be
4
4
4
a class of complexes with highly interesting magnetic
properties. In most cases, the superexchange interaction is
predominantly ferromagnetic, leading to a high-spin (S = 4)
ground state. The intramolecular magnetic interactions are
closely related to the Ni-O-Ni angles; they are ferromagnetic
for angles close to orthogonality and antiferromagnetic for
larger angles.
T
χ
3
2
0
50
100
150
200
250
300
T / K
-
1
Fig. 5 Plot of v
the best fit of the experimental data
M M
vs. T and v T vs. T for 3. The solid line represents
Concluding remarks
The best least squares fitting was obtained with J =
?
1
2
-
1
-1
18.45 cm , g = 2.39, D = 2.27 cm , and TIP =
The Schiff bases L and L contain three separate binding
subunits, each being able to coordinate one metal ion and
the phenol group; in their deprotonated forms, they have a
strong tendency to bridge the two metal ions. For this
reason, the two metal ions are forced to remain close to
each other, and the phenolate group plays a key role in
determining the molecular geometry of the binuclear spe-
cies. Moreover, because of the number of binding sites, the
ligand does not completely saturate the coordination sites
of the metal ions and the complexes formed can be used to
assemble at least one secondary ligand. This capability is
well illustrated in the crystal structures obtained here using
Ni(II) metal ions. In all cases, the Ni-Ni bond distances are
very close to each other. The magnetic behavior of com-
pounds 1–3 depends on the pseudohalide and methanolate
-
.17 9 10 cm mol
4
3
-1
-6
2
with R = 4.48 9 10
-1
for 1;
J = ? 17.09 cm , g = 2.44, D = 2.59 cm , and TIP =
-
1
-
5
3
1.24 9 10 cm mol
-1
-6
-
with R = 3.25 9 10
ðv Þ ꢁ ðv Þ
for 2
=
P ꢀ
ꢁ
2
(
R
value is defined as
2
M obs
M calc
P
½
ðv Þ ꢂ ). The positive J values demonstrate that Ni(II)
M obs
spins are coupled ferromagnetically.
The magnetic susceptibilities of complexes 3 shown in
Fig. 5 were measured at 0.1 T in the temperature range
2
.0–300 K. It also onsets ferromagnetic coupling between
Ni ions. The cryomagnetic behavior of 3 obeys the Curie–
Weiss law in the temperature region 50–300 K with
3
-1
C = 5.28 cm K mol , h = 1.8 K.
The data were analyzed by using the spin Hamiltonian
(
Eq. 1), where JA characterizes the exchange interactions
Ni -Ni A and Ni -Ni A with larger Ni-O-Ni angles, while
ligand which bridges the two nickel (II) atoms. The v T vs.
M
1
2
2
2
T plots reveal that compounds 1, 2 and 3 are ferromag-
netically coupled.
JB characterizes the remaining four pairwise interactions
Fig. 6).
(
^
^
^
^
^
^
^
^
^
H ¼ ꢁ 2JAðS1 ꢀ S2 þ S2 ꢀ S3Þ ꢁ 2JBðS1 ꢀ S3 þ S1 ꢀ S4
^
^
^
^
þ S3 ꢀ S4 þ S2 ꢀ S4Þ:
ð1Þ
Supplementary material
Thereafter, a ‘two J’ mode is employed to analyze the
Ni cluster (Ni-J -Ni-J -Ni-J -Ni) [37]. A least squares fit
CCDC 755211–755213 contain the supplementary crys-
tallographic data for compounds 1, 2 and 3, respectively.
These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
4
1
2
1
Acknowledgments We are grateful for financial support from the
Natural Science Foundation Council of China (NSFC) (grant No.
2
0401003) and 111 Project (B07012).
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